Method for production of microcapsule type conductive filler

ABSTRACT

A process for producing a MC-type conductive filler includes treating minute metallic particles with a coupling agent, preparing an oil phase of the coupling agent-treated minute metallic particles and a reactive substance A, the reactive substance A directly contacting the metallic particles. Then, an aqueous phase is prepared having a reactive substance B, which is capable of reacting with the reactive substance A, dissolved in water. Thereafter, the oil phase is dispersed in the aqueous phase to form a suspension. In situ reaction of the reactive substances A and B is then caused by applying heat to the suspension or adding a catalyst to the suspension. This forms a coating of a thermosetting insulating resin on the surface of the minute metallic particles. Alternatively, the reactive substance B may not be used. A MC-type conductive filler may also be made by immersing minute metallic particles in an affinity agent, immersing and dispersing the affinity agent treated-particles in an epoxy monomer and polymerizing the monomer to form an insulating polymer on the surface of the minute metallic particles.

This application is a continuation of application Ser. No. 08/372,904,filed Jan. 17, 1995, now abandoned, which is a continuation ofapplication Ser. No. 07/964,608, filed Oct. 23, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for the production of a microcapsule(MC) type conductive filler and more particularly to a method forcoating the surface of minute conductive particles with an insulatingpolymer and to an MC type adhesive agent having dispersed in an adhesiveagent the coated MC type conductive filler.

2. Description of the Related Art

In the conventional method of adhesion, the adhesion effected by softsoldering or welding where the interface produced by this adhesionrequires conductivity. The conventional method is effectively applicableonly to a limited number of materials because of the heat factor. Incontrast, the organic-inorganic composite conductive adhesive agent thatis composed of a binder using a synthetic resin as a main componentthereof and a conductive filler using a metal powder as a main componentthereof finds utility in a wide variety of applications that involvingdifferent kinds of materials subjected to adhesion. This adhesive agent,therefore, is an indispensable medium for conductive adhesion of plasticsubstances (such as epoxy and phenol resins) that do not adhere by softsoldering, for adhesion of NESA glass used in liquid crystal displaydevices, for adhesion of phosphor bronze with a carbon brush used inmicrometers, and for adhesion of lead wires as in quartz oscillators andsdc meters, for example.

Particularly, in the semiconductor industry, which has been enjoyingsignificant growth recently, IC's and LSI's of increasingly high qualityhave been developed and mass produced. For the adhesion of thesesemiconductor chips (silicon wafers) to lead frames, though the methodinvolving to an Au--Sn eutectic once prevailed, conductive adhesiveagents formed by kneading an epoxy resin with silver powder now havemultiple applications utility owing to their ability to lower cost andenhance productivity.

As a resin binder for conductive adhesive agents, while epoxy resin isgenerally used, polyimide type, phenol type, and polyester type resinsare also used, though only partially. As a conductive filler, minuteparticles of such metals as gold, silver, and copper and amorphouscarbon and graphite powder are generally used as well as metal oxides,though only partially. Silver powder is preferably used over theconductive fillers cited above because it is inexpensive, reliable andeffective.

The conductive adhesive agent is advantageous in various respectscompared with conventional applications such as soft soldering andwelding though it is not perfectly free from fault. When this conductiveadhesive agent is used between an LSI chip and patterns for mountingcomponent parts, for example, an increase in the amount of minuteconductive particles that are incorporated in the conductive adhesiveagent lowers insulation resistance as illustrated in FIG. 1 andincreases the possibility of adjacent patterns forming electriccontinuity. A reduction in the amount of minute conductive particlesreduces the electric continuity between the LSI and the patterns. Dataindicate the necessity for rigidly controlling the amount of minuteconductive particles to be used in the conductive adhesive agent. And atthe same time, reveal the fact that the minute conductive particlescannot be used in large amounts.

It is believed possible that this problem can be solved by a procedurethat comprises preparing an MC type conductive adhesive agent havingdispersed in an adhesive agent, an MC type conductive filler formed bycoating the surface of minute conductive particles with an insulatingpolymer, applying the MC type conductive adhesive agent to the entiresurface of the substrate of an IC or LSI chip, exerting pressure to bearon the interface between the chip and patterns deposited thereon,thereby rupturing the coating layer of the capsules and establishingelectric continuity between the chip and the patterns, and meanwhileallowing the encapsulated minute conductive particles interposed betweenthe adjacent patterns to remain intact and continue to insulate thesepatterns from one another.

The insulating resins that are usable for coating the surface of minuteconductive particles include thermoplastic resins and thermosettingresins as classified by kind. In terms of resistance to moistureabsorption and electric insulating properties, thermosetting resinsdefinitely excel thermoplastic resins. Since thermocompression bondingof a chip to a substrate is generally carried out at an elevatedtemperature of at least 170° C., the insulating resin to be used isrequired to be stable enough to resist this elevated temperature thoughfew thermoplastic resins can endure this temperature. In contrast, mostthermosetting resins can tolerate temperatures in the neighborhood of200° C.

For use as an insulating resin in the MC type conductive filler,thermosetting resins that are advantageous in various respects overthermoplastic resins are suitable.

For the application of an insulating resin coating to the surface ofminute conductive particles, however, the procedure that involvesdissolving the resin in a solvent, spraying the solution on the surfaceof the minute conductive particles, and drying the applied coating ofthe solution is predominant though since thermosetting resins areinsoluble in solvents, this procedure applied conventionally isdifficult and the application of a thermosetting resin coating to thesurface of minute conductive particles, therefore, necessitatesdevelopment of a novel coating procedure.

The prior techniques pertaining to the MC type conductive adhesive agenthave been disclosed by Japanese Unexamined Patent Publications No.176,139/1987, No. 76,215/1987, No. 47,943/1988, No. 54,796/1988, No.103,874/1990, and No. 103,875/1990, for example.

First, the disclosures of Japanese Unexamined Patent Publications No.176,139/1987, No. 76,215/1987, No. 47,943/1988, and No. 54,796/1988 willbe described. These patent publications disclose, as conductive adhesiveagents, those produced by forming an intermediate conductive layer onspherical cores of resin and coating the intermediate layer with asurface layer of an insulating thermoplastic resin and those produced bycoating the surface of minute spherical conductive particles with aninsulating thermoplastic resin. Actual mounting of a chip on a substratefor a printed circuit by using such a conductive adhesive agent isattained by a procedure that comprises applying the conductive adhesiveagent to the substrate and thermocompression bonding the chip to thesubstrate so that the intermediate layer or the minute conductiveparticles will discharge a conductive function and the insulatingthermoplastic resin an adhesive function and an insulating function. Thetechniques disclosed by these patent publications differ from the methodusing the MC type conductive adhesive agent of the present invention andthese patent publications do not mention using a thermosetting resin asan insulating resin for coating the surface of the minute conductiveparticles.

Now, the disclosure of Japanese Unexamined Patent Publication No.103,874/1990 will be described below. The invention of this patentpublication pertains to an MC type conductive adhesive agent produced bydispersing in a film of an insulating adhesive agent serving as a binderan MC type conductive filler having minute conductive particles coatedwith an insulating thermoplastic resin or thermosetting resin.Conductive union of two given members using this MC type conductiveadhesive agent is accomplished by depositing this adhesive agent on thetwo members and pressing the two members against each other while beingheated state. Thus, in the part expected to form electric continuity,the impact of the pressure exerted as described above ruptures theinsulating resin layer of the MC filler and establishes the desiredelectric continuity, whereas in the part requiring insulation, the MCtype conductive filler is allowed to remain intact and, therefore,retain stable insulation. Incidentally, this MC type conductive filleris manufactured by plasma polymerization or plasma CVD polymerizationand there are times when the insulating film of the MC type filler maybe formed of a thermosetting resin. The number of kinds of thermosettingresins that can be manufactured by the plasma polymerization and theplasma CVD polymerization is very small because the number of kinds ofgases usable for injection during the polymerization is not large.Further in accordance with this method of plasma polymerization orplasma CVD polymerization, the cost is sufficiently high to render themanufacturing thereof impracticable and productivity is inferior becausethe amount of MC type filler to be manufactured is small.

The disclosure of Japanese Unexamined Patent Publication No.103,875/1990 will be described below. The invention of this patentpublication pertains to the use of an MC type conductive adhesive agentproduced by coating minute conductive particles with an insulatingthermoplastic resin or thermosetting resin. Actual mounting of a chip ona substrate for a printed circuit using this MC type conductive adhesiveagent is attained by applying the conductive adhesive agent to thesubstrate and thermocompression bonding the chip to the substrate, withthe intermediate layer or the minute conductive particles discharging aconductive function and the insulating resin on the surface of theminute conductive particles an adhesive function and an insulatingfunction. Incidentally, this MC type conductive filler is manufacturedby either plasma polymerization or plasma CVD polymerization. Thus,these prior techniques are described as allowing what is formed bycoating the surface of minute conductive particles with a thermosettingresin. In spite of these disclosures, thermosetting resins should beunusable for the purpose of coating because they do not melt with heatand, therefore, are incapable of functioning as an adhesive. Even if athermosetting resin is used, the method of manufacturing the MC typeconductive filler entails a serious drawback as pointed out in JapaneseUnexamined Patent Publication No. 103,874/1990.

Practically all the prior techniques pertaining to the manufacture of anMC type conductive filler or the conductive adhesive agent using thisfiller invariably use a thermoplastic resin. Even when the patentpublications mention usability of a thermosetting resin, methods ofmanufacturing using such a thermosetting resin are not disclosed withsufficient specificity or are devoid of practicability and thus, thesemethods cannot be actually used.

SUMMARY OF THE INVENTION

This invention has been produced for the purpose of solving the problemsencountered by the prior art as described above. The first aspect ofthis invention, i.e. the method for production of an MC type conductivefiller is characterized by dispersing minute conductive particles (oilphase) allowing the presence of either both a solvent and a reactivesubstance A or the aforementioned reactive substance A alone on thesurface thereof in water having dissolved therein a reactive substance Bcapable of reacting with the reactive substance A (aqueous phase)thereby forming a suspension or causing either a solvent and at leastone reactive substance or, as aforementioned, at least one reactivesubstance alone to be present on the surface of minute conductiveparticles (oil phase) and dispersing the minute conductive particles inwater thereby forming a suspension and applying heat or adding acatalyst to the suspension thereby inducing the reactive substance toreact on the surface of the minute conductive particles thereby forminga thermosetting, thermoplastic, or combined thermosetting-thermoplasticinsulating resin.

The second aspect of this invention, i.e. the MC type conductiveadhesive agent is produced by dispersing in an adhesive agent an MC typeconductive filler that is produced by dispersing minute conductiveparticles (oil phase) allowing the presence of either a solvent and areactive substance A both or the aforementioned reactive substance Aalone on the surface thereof in water having dissolved therein areactive substance B capable of reacting with the reactive substance A(aqueous phase) thereby forming a suspension or causing either a solventand at least one reactive substance or, as aforementioned, at least onereactive substance alone to be present on the surface of minuteconductive particles (oil phase) and dispersing the minute conductiveparticles in water thereby forming a suspension and applying heat oradding a catalyst to the suspension thereby inducing the reactivesubstance to react on the surface of the minute conductive particlesthereby forming a thermosetting, thermoplastic, or combinedthermosetting-thermoplastic insulating resin.

The term "reactive substance" as used in this specification refers to asubstance that is capable of forming an insulating polymer on thesurface of a filler either by itself or through reaction with anotherreactive substance. The substances that answer this description includemonomer components, oligomer components, and polymer components thatform an insulating polymer, for example.

The third aspect of this invention, i.e. the method for production of anMC type conductive filler comprises (a) a step of immersing minuteconductive particles in an affinity agent thereby treating the surfaceof the minute conductive particles, (b) a step of immersing anddispersing the surface-treated minute conductive particles in an epoxymonomer thereby forming a suspension, and (c) a step of polymerizing themonomer in the suspension thereby forming a thermosetting insulatingpolymer on the surface of the minute conductive particles.

The fourth aspect of this invention, i.e. the MC type conductiveadhesive agent, is produced by dispersing in an adhesive agent the MCconductive filler obtained by the method described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects and advantages otherthan those set forth above will become apparent when consideration isgiven to the following detailed description thereof. The descriptionmakes reference to the annexed drawings wherein:

FIG. 1 is a graph showing the relation between insulation resistance andconductivity with the amount of minute conductive particles as aparameter,

FIG. 2 is a flow sheet of the production of a microcapsule typeconductive filler,

FIG. 3 is a type diagram of the microcapsule type conductive filler,

FIG. 4 is a type diagram illustrating one example of a substrate,

FIG. 5 is a type diagram illustrating one example of a glass chip,

FIG. 6 is a type diagram illustrating sites for determination ofelectric continuity resistance and insulation resistance,

FIG. 7 is a partially magnified diagram of FIG. 6,

FIG. 8 is a photomicrograph of the microcapsule type conductive filler(15,000 magnifications),

FIG. 9 is a photomicrograph of a part of union between a bump and a pad(504 magnifications),

FIG. 10 is a type diagram illustrating the state of union between a chipand a substrate,

FIG. 11 is a flow sheet of the production of a microcapsule typeconductive filler as the second aspect of this invention,

FIG. 12 is a type diagram illustrating a growth model of a triazinethiol film on the surface of metal, and

FIG. 13 is a type diagram illustrating the reaction mechanism of anepoxy monomer with triazine thiol.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principle for the production of an MC conductive filler will bedescribed below.

(Production using one kind of monomer)

A suspension is produced by dispersing minute conductive particleshaving the surface thereof treated with a coupling agent in a solutionof a monomer and a reaction initiator (oil phase) and adding theresultant dispersion dropwise to water having an emulsifier and aviscosity enhancer dissolved therein (aqueous phase). By applying heatto this suspension, for example, the monomer is polymerized in situ onthe surface of the minute conductive particles and allowed to form acoating thereon. Examples of the monomer that is usable singly hereinare divinyl benzene and acryl. A thermosetting polymer is obtained fromdivinyl benzene monomer and a thermoplastic polymer from acryl monomer.

(Production using two or more kinds of monomers)

A suspension is produced by dispersing minute conductive particleshaving the surface thereof treated with a coupling agent in the solutionof a monomer in a solvent (oil phase) and adding the resultantdispersion dropwise to water having another monomer, an emulsifier, anda viscosity enhancer dissolved therein (aqueous phase). By applying heator adding a catalyst to this suspension, the monomers are interfaciallypolymerized on the surface of the minute conductive particles andallowed to coat the minute conductive particles. The coating can bealternatively effected by preparing a suspension having at least twokinds of monomers dissolved in the oil phase and subjecting the monomersto in situ polymerization. Examples of the monomers that are usable inthe form of a combination of two monomers herein are epoxy/amine andbismaleimide/amine (both producing a thermosetting polymer).

In the production of the MC conductive filler, the following points mustbe taken into consideration.

(1) The minute conductive particles should be treated in advance with acoupling agent. (2) The sp value of the coupling agent to be used forthis treatment should be within ±10 (cal/cm³)^(1/2) of that of themonomer to be used. (3) The viscosity of the aqueous phase should be inthe range between 20 and 10,000 cps. (4) The suspension should bestirred at a rate in the range between 50 and 250 rpm to effect thereaction of the monomer. The reason for (1) is that since themonomolecular film of the coupling agent on the surface of the minuteconductive particles and the monomer molecules are intertwined, themonomer is retained on the surface of the minute conductive particlesand the coating is effected uniformly. The reason for (2) is that if thesp value deviates from the range of ±10 (cal/cm³)^(1/2), the monomer isnot thoroughly intertwined with the coupling agent and it is retained onthe surface of minute conductive particles with difficulty. The reasonfor (3) is that the minute conductive particles settle and agglomerateif the viscosity is less than 20 cps and the separation of the MC typeconductive filler after completion of the coating is not obtained if theviscosity exceeds 10,000 cps. The reason for (4) is that the minuteconductive particles settle and agglomerate during the reaction of themonomer if agitation is omitted.

The minute conductive particles to be used for this method of productionof the filler are only required to be made of a conductive metallicmaterial. The kind of metallic material is irrespective. For example,minute Cu particles having the surface thereof coated with Ag or minuteAg particles are preferably used.

The minute conductive particles are preferably spheres or pseudospheresin shape. These minute conductive particles preferably have a diameterof not more than 50 μm.

The insulating layer of a thermosetting resin for the MC type conductivefiller is preferably made of a cured epoxy/amine or bismaleimide/aminetype resin. The insulating layer of thermosetting resin of the MC typeconductive filler preferably has a thickness of not more than 3 μm.

This invention pertains in one aspect of an MC type conductive adhesiveagent having dispersed in an adhesive agent the filler obtained asdescribed above. The adhesive agent that can be effectively used in theMC type conductive adhesive agent is the same as mentioned above. Forexample, an epoxy type one-component polyimide or polyester adhesiveagent is preferably used.

The viscosity of the adhesive agent mentioned above is preferably notmore than 150,000 cps. The content of the MC type conductive filler inthe MC type conductive adhesive agent is preferably not more than 50% byvolume.

One preferred embodiment of the method of this invention comprisesforming a suspension by uniformly dispersing minute conductive particlesallowing the presence of a solvent and a monomer (monomer A) on thesurface thereof in water having another monomer (monomer B) dissolvedtherein and applying heat to the suspension thereby inducing the twomonomers to react on the surface of the minute conductive particles andform an insulating polymer and consequently producing a microcapsuletype filler. In this method, the monomer A and the monomer B are monomercomponents that are intended to form an insulating polymer. When apolyamide is intended to form the insulating polymer, for example,adipic acid dichloride serves as the monomer A and hexamethylene diamineas the monomer B. Where polyurethane is intended to form the insulatingpolymer, for example, tetramethylene diisocyanate serves as the monomerA and methamethylene glycol as the monomer B.

The solvents that are effectively usable for dissolving the monomer Ainclude dichloroethane, chloroform, carbon tetrachloride, xylene,toluene, benzene, dichloromethane, and ethyl acetate, for example. Thesuspension is heated for the purpose of promoting the reaction of themonomers therein. The temperature of this heating is in the rangebetween normal room temperature and boiling point of the solvent. It isselected in accordance with the particular quality of the suspension tobe heated.

In the method described above, the minute conductive particles must betreated with a coupling agent before using. This treatment serves thepurpose of fixing the monomer A on the minute conductive particles.

Further, in the method described above, the viscosity of the aqueousphase having the monomer B dissolved therein is preferably adjusted soas to fall in the range between 20 and 10,000 cps by the addition of aviscosity enhancer. During the application of heat to the suspensionmentioned above, the suspension must be stirred at a rate in the rangebetween 50 and 250 rpm for reacting the two monomers.

The monomers are preferably used in an amount that is at leastsufficient for the monomers to form a film of not less than 0.05 μm inthickness on the surface of the minute conductive particles.

Now, the present invention will be described in detail below withreference to working examples. Of course, this invention is not limitedto the working examples.

The affinity enhancer such as triazine thiol, which is used at the step(a) in the method, i.e. the third aspect of this invention, allowseffective polymerization of the monomers because it is capable ofinducing uniform adhesion of the epoxy resin monomer to the surface ofthe minute metallic particles and opening the heterocycles in the resin.The concentration of triazine thiol should not be more than 10⁻³mol/liter. As a result, the heretofore difficult coating of the surfaceof the minute conductive particles with the thermosetting resin can beeasily attained by the method of this invention. Further, since thecoating film of the thermosetting resin is superior to the coating filmof a thermoplastic resin in strength, the MC type conductive filler canbe incorporated in a large amount in the adhesive agent and the MC typeconductive adhesive agent consequently produced can effect an adhesiveunion of two given members with higher reliability than the conventionaltechnique.

Now, this invention will be described more specifically below withreference to working examples, which are illustrative of and notlimitative in any sense of this invention.

Examples 1 to 13 and Comparative Examples 1 to 3 cited hereinbelowpertain to the first and second aspects of this invention.

EXAMPLE 1

A microcapsule type conductive adhesive agent was produced with thefollowing materials.

Minute conductive particles: Minute pseudospheres of Cu having thesurface thereof plated with Ag (Ag/Cu, average diameter 5 μm).

Dispersant: Titanate type coupling agent.

Monomers: Bisphenol A type epoxy (BPA) and tetraethylene pentamine(TEPA).

Adhesive agent: Epoxy type one-component adhesive agent.

(1) Production of Microcapsule Type Conductive Filler (using a monomerand a solvent respectively in oil phase and aqueous phase).

Coating of silver powder with cured BPA and TEPA.

An aqueous phase was prepared by dissolving 25 g of polyvinyl alcohol, 2g of an emulsifier, and 10 g of TEPA in 400 ml of water. An oil phasewas prepared by dissolving 7 g of BPA in 15 ml of dichloroethane andadding to the resultant solution 15 g of silver powder treated with atitanate type coupling agent in accordance with the flow chartillustrated in FIG. 2. By exposing the oil phase to an ultrasonic wavefor 20 minutes, the silver powder agglomerated therein was dispersed.Then, the aqueous phase was stirred with a homogenizer at a rate of3,000 rpm and, at the same time, the oil phase was gradually addeddropwise to the stirred aqueous phase to produce a suspension allowingthe presence of the oil phase on the surface of the silver powder. Thissuspension was kept at 60° C. and stirred with a three-one motor at arate of 180 rpm for four hours. Thereafter, a microcapsule typeconductive filler A having the surface of minute conductive particles(silver powder) coated with a polymer as illustrated in FIG. 3 wasseparated and dried at 60° C. for 30 minutes, to afford an MC typeconductive filler.

Since the production of this MC type conductive filler forms the subjectmatter of this invention, the production of the MC type filler set forthin Example 1 above will be described more specifically below (in thefollowing description, the amounts of part of the raw materials aredifferent from those of the preceding paragraph).

1.1 Treatment of Fine Metallic Particles with a Coupling Agent

To ensure retention of the monomer on the surface of fine metallicparticles, the following treatment with a coupling agent was carriedout. In 50 ml of ethanol, 0.3 g of a titanate type coupling agent and 6g of minute Ag/Cu particles were retained at 60° C. and subjected toultrasonic dispersion for 10 minutes. Then, by keeping the solution at60° C. and expelling ethanol by distillation, the treatment of thesurface of minute metallic particles with the coupling agent waseffected. Incidentally, the amount of coupling agent to be used must bein the range between 0.1 and 10% by weight and is preferably 5% byweight, based on the amount of the minute metallic particles. The reasonfor the particular range is that the surface of the minute metallicparticles cannot be uniformly coated with the coupling agent if theamount is less than 0.1% by weight and the minute metallic particlescohere if the amount exceeds 10% by weight. Further, the solubilityparameter of the coupling agent is desired to be within ±10(cal/cm³)^(1/2) of that of the monomer to be used in the oil phase. Thisrange is important for the purpose of improving the molecularintertwining of the coupling agent and the monomer.

1.2 Preparation of Aqueous Phase

An aqueous phase was prepared by dissolving 1.5 g of an emulsifier, 14.5g of PVA (viscosity of the aqueous phase 20 cps), and 10 g of TEPA in200 ml. Here, the amount of PVA to be added must be controlled so as toadjust the viscosity of the aqueous phase in the range between 1 and1,000 cps and preclude the otherwise possible sedimentation of theminute metallic particles.

1.3 Preparation of Oil Phase

An oil phase was prepared by dissolving 10 g of BPA in 30 ml of ethylacetate and adding 7 g of minute Ag/Cu particles to the resultantsolution. The solvent to be used for the oil phase must exhibitsolubility of not less than 0.1% in water. If a solvent not satisfyingthis condition is used, the solvent in the produced MC filler intervenesbetween the polymer and the minute metallic particles and, when this MCfiller is used in the conductive adhesive agent, the entrapped solventcauses corrosion of the product of union. The solubility of the solventto be used is preferably about 3% in water.

1.4 Dispersion of Minute Ag/Cu Particles

The oil phase was exposed to an ultrasonic wave for 10 minutes to effectthorough dispersion of the minute Ag/Cu particles therein. Though theminute Ag/Cu particles used in this example were spheres in shape, thecoating is equally effected when these particles are pseudospheres orfish scales in shape. When the MC filler is intended for use in the MCtype conductive adhesive agent, the particles in the shape of fishscales are not used advantageously because they do not serve as spacersbetween the bump and the pad as shown in Table 8.

1.5 Preparation of Suspension

A suspension was prepared by stirring the aqueous phase with ahomogenizer at a rate of 4,000 rpm and, at the same time, adding the oilphase gradually to the stirred aqueous phase dropwise. The operatingspeed of the homogenizer must be in the range between 500 and 10,000rpm. The reason for the particular range is that no homogeneoussuspension is obtained if the speed is less than 500 rpm and the minuteAg/Cu particles are damaged if the speed exceeds 10,000 rpm.

1.6 Interfacial Polymerization Reaction

The suspension prepared in 1.5 above was stirred with a three-one motorat 150 rpm and heated at 60° C. to induce a reaction for four hours. Thestirring must be carried out with an operational speed kept in the rangebetween 50 and 250 rpm., which prevents sedimentation of the minutemetallic particles (to which occurs if the speed is less than 50 rpm),cohesion (which occurs if the speed is larger than 250 rpm) during theinterfacial polymerization reaction.

(2) Observation of Cross Section of Microcapsule Type Conductor Filler

The microcapsule type conductive filler produced as described above wasburied in an epoxy resin, allowed to set therein, and cut with amicrotome to expose the cross section of the filler for visualobservation.

(3) Confirmation of Insulation of Microcapsule Type Conductive Filler

The filler was dispersed between two opposed glass substrates having thesurface thereof coated with ITO and tested for insulation between theglass substrates.

(4) Preparation of Conductive Adhesive Agent

The microcapsule type conductive filler prepared in (1) above was mixedin a voluminal proportion of 20% with an epoxy type one-componentadhesive agent. The resultant mixture was thoroughly stirred to effectdispersion of the filler therein to afford a microcapsule typeconductive adhesive agent.

(5) Bonding of Chip to Substrate

A 40 μm conductive adhesive agent prepared in (2) above was uniformlyapplied to a substrate (number of pads 128, interval between pads 100μm, and size pad 200 μm □) illustrated in FIG. 4. The substrate and aglass chip (128 pins) illustrated in FIG. 5 to which the substrate wastacked by bumping were subjected to thermocompression bonding at atemperature of 170° C., 30 sec, and 35 g/bump. In the diagram of FIG. 4,2 represents an electrode and 4 represents an electrode to be used forsuch evaluations as a test for electric continuity.

(6) Test for Electric Continuity and Test for Insulation

The product of union obtained by bonding in (3) above was tested forelectric continuity by the four-terminal method using the sites ofmeasurement illustrated in FIG. 6 and FIG. 7 and was tested forinsulation by using a high-resistance meter (insulation resistancemeter).

Incidentally, the measurement of electric continuity was made at circuit1, circuit 2, circuit 3, and circuit 4 and that of insulation resistanceat insulation part 1, insulation part 2, and insulation part 3 asillustrated in FIG. 7.

(7) Observation of State of Adhesion of Chip to Substrate

The product of union obtained by bonding in (3) above was sectioned andthe cross section consequently exposed was visually examined todetermine the state of adhesion of the filler to the chip and thesubstrate.

(Results)

(1) Observation of Cross Section of Microcapsule Type Conductive Filler

FIG. 8 is a photograph of a cross section of the microcapsule typeconductive filler. It is clearly noted from the photograph that aninsulating polymer was present on the surface of a minute conductiveparticle, indicating that the particle was completely coated.

(2) Confirmation of Insulation with Microcapsule Type Conductive Filler

The two opposed glass substrates were found to be insulated from eachother, indicating that the microcapsule type conductive filler served toeffect insulation.

(3) Measurement of Electric Continuity

The results of the test for electric continuity are shown in Table 1.All the circuits used for the test invariably showed highly satisfactoryresults of electric continuity not exceeding 1.5 Ω (not more than 0.2 Ωper joint).

To be specific, the chip and the substrate were joined as illustrated inFIG. 10 and the electric continuity resistance was not more than 0.2 Ωper joint and, in spite of the high filler content of 20% by volume, theadjacent patterns showed highly satisfactory insulation in the order of1×10¹¹ Ω.

                  TABLE 1                                                         ______________________________________                                        Electric continuity resistance                                                Side of measurement                                                                        Circuit 1                                                                              Circuit 2                                                                              Circuit 3                                                                            Circuit 4                               ______________________________________                                        A            1.1034   1.1298   1.0865 1.2051                                  B            1.1298   1.2114   1.1695 1.1326                                  C            1.2365   1.1511   1.1233 1.1519                                  D            1.2562   1.1145   1.2314 1.1413                                  ______________________________________                                         In:                                                                      

(4) Measurement of Insulation Resistance

Table 2 shows the results of the test for insulation resistance. Eventhough the amount of filler incorporated was as large as 20% by volume(substantially equal to the amount of silver paste for a die bond), theadjacent patterns displayed highly satisfactory insulation of not lessthan 10¹¹ Ω.

                  TABLE 2                                                         ______________________________________                                        Insulation resistance                                                         Side of measurement                                                                       Insulation 1                                                                             Insulation 2                                                                             Insulation 3                                ______________________________________                                        A           3.6        2.5        2.8                                         B           2.1        2.6        3.0                                         C           1.5        2.7        3.0                                         D           1.8        2.0        3.0                                         ______________________________________                                         In: 10.sup.11                                                            

(5) Observation of State of Union Between Chip and Substrate (bump andpad)

FIG. 9 is a photograph showing a cross section of the joint between thebump and the pad. It is clearly noted from this photograph that themicrocapsule type conductive filler was amply present between the bumpand the pad.

EXAMPLE 2

A microcapsule type conductive filler was produced by faithfullyfollowing the procedure of Example 1, except that minute Ag particles(average diameter 0.1 μm) were used instead as minute conductiveparticles. It was evaluated in the same manner as in Example 1.

(Results)

(1) Observation of Cross Section of Microcapsule Type Conductive Filler

Similarly to the filler illustrated in FIG. 8, an insulating polymer wasfound to have uniformly coated the surface of agglomerated minuteconductive particles.

(2) Confirmation of Insulation with Microcapsule Type Conductive Filler

The filler showed the same degree of insulation as found in Example 1.

(3) Measurement of Electric Continuity Resistance

The electric continuity resistance was substantially the same as inExample 1.

(4) Measurement of Insulation Resistance

The insulation resistance was substantially the same as in Example 1.

(5) Observation of State of Union Between Chip and Substrate (bump andpad)

Similarly to the product of union illustrated in FIG. 9, themicrocapsule type conductive filler was amply present between the padand the bump.

EXAMPLE 3

Microcapsule type conductive filler and adhesive agent were produced byfaithfully following the procedure of Example 1, except that 10 g ofbismaleimide (BMI) and 0.1 g of diazobicycloundecene were used in placeof the monomer BPA. They were evaluated in the same manner as in Example1.

(Results)

(1) Observation of Cross Section of Microcapsule Type Conductive Filler

Similarly to the product of union illustrated in FIG. 8, an insulatingpolymer was found to have coated minute conductive particles completely.

(2) Confirmation of Insulation with Microcapsule Type Conductive Filler

The filler showed the same degree of insulation as in Example 1.

(3) Measurement of Electric Continuity Resistance

The filler showed the same degree of electric continuity resistance asin Example 1.

(4) Measurement of Insulation Resistance

The filler showed the same degree of insulation resistance as in Example1.

(5) Observation of State of Union Between Chip and Substrate (bump andpad)

The state of union was the same as that found in Example 1.

COMPARATIVE EXAMPLE 1

(1) Preparation of Microcapsule Type Conductive Filler

A microcapsule type conductive filler was produced by the coating methoddescribed below using the following materials.

Minute conductive particles: 30 g of minute Ag/Cu particles (same asthose of Example 1)

Polymer: PMMA (average particle diameter 0.15 μm) (m.p. 135° C.)

A microcapsule type conductive filler coated with PMMA was produced bydissolving 5 g of PMMA in 100 ml of xylene, spraying the resultantsolution into minute conductive particles, and drying the particles (forexpulsion of xylene).

(2) Observation of cross section of microcapsule type conductive filler

(3) Confirmation of insulation with microcapsule type conductive filler

(4) Preparation of conductive adhesive agent

(5) Bonding of chip to substrate

(6) Test for electric continuity and test for insulation

(7) Observation of state of union between bump and pad

The operations of (2) to (7) indicated above were carried out in thesame manner under the same conditions as those of (2) to (7) of Example1.

(Results)

(1) Observation of Cross Section of Microcapsule Type Conductive Filler

Similarly to the minute conductive particles of (7), Example 1illustrated in FIG. 8, the filler particles were found to be completelycoated with PMMA.

(2) Confirmation of Insulation with Microcapsule Type Conductive Filler

Similarly to the filler of Example 1, the microcapsule type conductivefiller retained insulation.

(3) Measurement of Electric Continuity Resistance

All the circuits, similarly to those of Example 1, showed highlysatisfactory electric continuity resistance of not more than 1.5 Ω.

(4) Measurement of Insulation Resistance

Table 3 shows the results of the measurement. Of the total of 12insulation parts, two insulation parts showed electric continuity,probably because the bonding was made at a temperature of 200° C. andthe PMMA was consequently decomposed or fused to establish contactbetween the minute conductive particles.

                  TABLE 3                                                         ______________________________________                                        Insulation resistance                                                         Side of measurement                                                                       Insulation 1                                                                             Insulation 2                                                                             Insulation 3                                ______________________________________                                        A           1.5        2.5 × 10.sup.11                                                                    510                                         B           2.1 × 10.sup.11                                                                     8         150                                         C           20         2.7 × 10.sup.11                                                                     26                                         D           35         10         3.0 × 10.sup.11                       ______________________________________                                         In:                                                                      

(5) State of Union Between Bump and Pad

Similarly to the results of (5) in Example 1, the microcapsule typeconductive filler was amply present between the bump and the pad.

COMPARATIVE EXAMPLE 2

Preparation of Microcapsule Type Conductive Filler

A microcapsule type conductive filler was produced by faithfullyfollowing the procedure of Example, except that Cu particles 60 μm indiameter were used as minute conductive particles.

The produced microcapsule type conductive filler was evaluated in thesame manner under the same conditions as described in (2) to (7) ofExample 1.

(Results)

The produced filler having the surface thereof completely coated with apolymer showed insulation. The electric continuity resistance and thestate of union between the bump and the pad were equal to those obtainedin Example 1. No insulation was retained between the adjacent pads.

COMPARATIVE EXAMPLE 3

A microcapsule type conductive filler produced by following theprocedure of Example 1 was mixed with an epoxy type adhesive agenthaving a viscosity of 210,000 cps.

(Results)

The filler could not be dispersed in the adhesive agent because theviscosity of the adhesive agent was unduly high.

EXAMPLE 4

The use of two kinds of monomers, a thermosetting resin, and a solventwas omitted and a monomer were used in both the oil phase and theaqueous phase.

A microcapsule type conductive filler and a microcapsule type conductiveadhesive agent were produced by faithfully following the procedure ofExample 1, except that an oil phase obtained by dispersing 7 g ofconductive particles treated with a coupling agent in 10 g of BPA inaccordance with the flow sheet shown in FIG. 2 was used dichloroethaneinstead of ethyl acetate solvent in the oil phase. They were evaluatedin the same manner as in Example 1.

(Results)

In all the items of evaluation, the results were equal to those obtainedin Example 1.

EXAMPLE 5

One kind of monomer was used and a thermosetting resin and a solventwere used, and one kind of monomer was used in the oil phase.

A microcapsule type conductive filler and a microcapsule type conductiveadhesive agent were produced by following the procedure of Example 1,except that an aqueous phase was prepared by dissolving 12 g ofpolyvinyl alcohol and 1.5 g of an emulsifier in 200 ml of water and asolution of 10 g of divinyl benzene and 0.1 g of benzoyl peroxide in 15ml of ethyl acetate was used as an oil phase.

(Results)

In all the items of evaluation, the results were almost the same asthose obtained in Example 1.

EXAMPLE 6

Two kinds of monomers were used, including a thermosetting resin and asolvent, and two kinds of monomers were used in the oil phase.

A microcapsule type conductive filler and a microcapsule type conductiveadhesive agent were produced by following the procedure of Example 1,except that an aqueous phase was prepared by dissolving 12 g ofpolyvinyl alcohol and 1.5 g of an emulsifier in 200 ml of water and anoil phase was prepared with 15 ml of ethyl acetate and 5 g of imidazole.They were evaluated in the same manner as in Example 1.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 7

Two kinds of monomers and a thermosetting resin were used only in theoil phase and no solvent was used.

An MC filler and an MC conductive adhesive agent were produced byfaithfully following the procedure of Example 6, except that the use ofethyl acetate was omitted. They were evaluated in the same manner as inExample 6.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 8

One kind of monomer and a thermosetting resin were used and no solventwas used. The monomer was used in the oil phase.

A microcapsule type conductive filler and a microcapsule type conductiveadhesive agent were produced by following the procedure of Example 2,except that an aqueous phase was prepared by dissolving 12 g ofpolyvinyl alcohol and an emulsifier in 200 ml of water and an oil phasewas prepared by dispersing in 10 g of divinyl benzene 0.1 g of benzoylperoxide and 7 g of minute conductive particles treated with a couplingagent in accordance with the flow sheet illustrated in FIG. 2 withoutusing ethyl acetate (solvent). They were evaluated in the same manner asin Example 2.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 9

A blend of a thermoplastic resin and a thermosetting resin and a solventwere used. The monomer was used in the oil phase.

A microcapsule type conductive filler and a microcapsule type conductiveadhesive agent were produced by following the procedure of Example 1,except that 5 g of methyl methacrylate, 5 g of bismaleimide, and 0.1 gof azoisobutyronitrile were used as monomers in place of BPA and TEPA.They were evaluated in the same manner as in Example 1.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 10

A blend of a thermoplastic resin and a thermosetting resin and a solventwere used. The monomer was used in the oil phase and the aqueous phase.

A microcapsule type conductive filler and a microcapsule type conductiveadhesive agent were produced by following the procedure of Example 1,except that an aqueous solution was prepared by dissolving 12 g ofpolyvinyl alcohol, 1.5 g of an emulsifier, and 15 g of hexamethylenediamine in 200 ml of water and a solution of 7 g of adipic acid and 7 gof BPA in 15 ml of ethyl acetate was used as an oil phase. They wereevaluated in the same manner as in Example 1.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 11

A blend of monomers was used in the oil phase and no solvent was used.

An MC filler and an MC type conductive adhesive agent were produced byfollowing the procedure of Example 10, except that ethyl acetate wasomitted. They were evaluated in the same manner as Example 10.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 12

A blend of monomers was used in the oil phase and the aqueous phase andno solvent was used.

An MC type filler and an MC type conductive adhesive agent were producedby following the procedure of Example 11, except that ethyl acetate wasomitted. They were evaluated in the same manner as in Example 11.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 1.

EXAMPLE 13

An MC type filler produced by the procedure of Example 1 was tested forthe following items.

(1) Effect of sp (solubility parameter) Value of Coupling Agent onProduction of MC Type Filler

Table 4 shows the results of the test performed on MC fillers preparedusing coupling agents of different sp values with respect to electriccontinuity.

                  TABLE 4                                                         ______________________________________                                        Results of test of MC type filler                                             for insulation                                                                Difference of sp values of                                                                          Results of test for                                     coupling agent and monomer                                                                          insulation                                              ______________________________________                                        0                     Insulation                                              5                     Insulation                                              10                    Insulation                                              11                    Electric continuity                                     ______________________________________                                    

The results indicate that the difference between the sp value of themonomer (epoxy resin) and the sp value of the coupling agent must bewithin 10 (cal/cm³)^(1/2). The possible reason for this limit is thatthe monomer molecules and the coupling agent molecules are intertwinedwith difficulty and retention of the monomer on the surface of theminute conductive particles is not attained. Incidentally, the sp valueof the epoxy resin is 10.9 (cal/cm³)^(1/2).

(2) Effect of Viscosity of Aqueous Phase on Stability of Suspension

Table 5 shows the results of the test performed involving the effect ofchanges in the viscosity of the aqueous phase on the stability of thesuspension.

                                      TABLE 5                                     __________________________________________________________________________    Relation between viscosity of                                                 aqueous phase and suspension                                                  Viscosity                                                                     of aqueous                                                                    phase (cps)                                                                          10   20   100 1000 10000                                                                              11,000                                         __________________________________________________________________________    Stability                                                                            Sediment-                                                                          Stable                                                                             Stable                                                                            Stable                                                                             Stable                                                                             Suspension not                                 of     ation of                producible and                                 suspension                                                                           minute                  separation of                                         conductive              MC filler after                                       particles               reaction not                                          observed                effectible                                     __________________________________________________________________________

The results indicate that the viscosity of the aqueous solution isproper in the range between 20 and 10,000 cps.

(3) Effect of Stirring Speed on Stability of Suspension

Table 6 shows the results of the test performed involving the effect ofthe stirring speed (30, 50, 250, and 300 rpm) on the stability of thesuspension.

                  TABLE 6                                                         ______________________________________                                        Relation of speed of stirring and                                             stability of suspension                                                       Speed of                                                                      stirring                                                                              30         50      250   300                                          ______________________________________                                        Stability                                                                             Sedimentation                                                                            Stable  Stable                                                                              Adhesion of minute                           of      of minute                conductive particles to                      suspension                                                                            conductive               beaker wall observed                                 particles                                                                     observed                                                              ______________________________________                                    

The results indicate that the stirring must be carried out at a rate ina range between 50 and 250 rpm.

(4) Relation of Particle Diameter and Insulation Resistance of MinuteConductive Particles

Table 7 shows the results of the test performed on minute conductiveparticles of diameters 10, 30, 50, and 70 μm for insulation.

                  TABLE 7                                                         ______________________________________                                        Relation between particle diameter                                            and insulating property of coated minute                                      conductive particles                                                          Particle diameter (μm) of                                                                       Results of test for                                      minute conductive particles                                                                        insulation                                               ______________________________________                                        10                   Insulation                                               30                   Insulation                                               50                   Insulation                                               70                   Electric continuity                                      ______________________________________                                    

The results indicate that the minute conductive particles to be usedshould have a diameter of not more than 50 μm.

(5) Relation Between Shape and Electric Continuity Resistance of MinuteConductive Particles.

Table 8 shows the results of the test performed on minute conductiveparticles having different shapes of spheres, pseudospheres, and fishscales with respect to electric continuity.

                  TABLE 8                                                         ______________________________________                                        Relation between shape and                                                    conductivity of minute conductive particles                                   Shape of minute                                                                            Conductivity (Number of defective                                conductive particles                                                                       portions/number of sites of measurement)                         ______________________________________                                        Spheres      0/100                                                            Pseudospheres                                                                              0/100                                                            Fish scales  23/100                                                           ______________________________________                                    

In the case of a filler using minute particles of the shape of fishscales, the surface completely coated with a polymer, the insulation wassatisfactory, and the adjacent pads were insulated from each other.Absolutely no electric continuity was established. Though the filler waspresent between the bump and the pad, it failed to serve as a medium forunion thereof. The results indicate that the minute conductive particlesshould be in the shape of either spheres or pseudospheres.

(6) Relation Between Thickness and Electric Continuity Resistance of anInsulating Resin Layer

Table 9 shows the results of the test performed on insulating resinlayers formed of the MC type conductive filler with differentthicknesses with respect to electric continuity.

                  TABLE 9                                                         ______________________________________                                        Relation between thickness and                                                conductivity of insulating resin                                              Thickness (μm) of                                                                       Resistance per site of measurement                               insulating resin                                                                           (Ω)                                                        ______________________________________                                        0.1          0.1                                                              2.0          0.4                                                              3.0          0.5                                                              4.0          1.5                                                              ______________________________________                                    

It is noted from Table 9 that the resistance to electric continuity washigh and points of poor electric continuity were detected when thethickness of the insulating resin layer (coating layer) was 4.0 μm. Theresults indicate that the thickness of the insulating resin layer isdesired to be not more than 3 μm.

(7) Content of MC Type Filler

Table 10 shows the relation between the MC type filler and the state ofcuring of the adhesive agent.

                  TABLE 10                                                        ______________________________________                                        Content of MC type conductive                                                 filler and state of adhesive agent                                            Content (%)                                                                           1      10     30   50   55   65     70                                ______________________________________                                        State of                                                                              Good   Good   Good Good Good Poor   Poor                              curing                               adhesion                                                                             adhesion                          ______________________________________                                    

Poor adhesion: Complete wetting of filler with adhesive agent notobtained because of excess amount of filler.

The results indicate that the content of the MC type conductive fillermust not be more than 60% by volume. Now, the third and fourth aspectsof this invention will be described specifically below with reference toExamples 14 to 16.

EXAMPLE 14

An MC type conductive adhesive agent was produced with the followingmaterials.

Minute conductive particles: Minute Cu pseudospheres having the surfaceplated with Ag (Ag/Cu, average particle diameter 5 μm).

Adhesive agent: A composition consisting of an epoxy resin as the maincomponent and an acid anhydride as the curing agent).

Affinity agent: Triazine thiol (RTD).

Monomer: Bisphenol A type epoxy resin (BPA) (produced by Shell andmarketed under trademark designation of "Epikote 828").

(1) Method for Production of MC Type Conductive Filler

The minute metallic particles were subjected to a surface treatment.First, the minute metallic particles were washed with an acid and thenwith an alkali, and pretreated with Triclene to defat and clean thesurface thereof. The cleaned minute metallic particles were immersed ina triazine thiol solution to be coated with a film of triazine thiol.This solution was prepared by dissolving triazine thiol in acetone in aconcentration of 10⁻⁴ mol/lit. No uniform film is obtained if theconcentration is lower than this level and the speed of treatment is toohigh to be controlled as required if the concentration exceeds 10⁻³mol/l. The temperature of this treatment is not lower than 17° C. It isdesired to be in the range of 20±3° C. because the speed of thetreatment is too high to be controlled as desired if the temperature isunduly high. The time of treatment is desired to be in the range of 30±5minutes in due consideration of the relation between the concentrationmentioned above and the temperature. It goes without saying that forsuch conditions as concentration, temperature, and time of thetreatment, the magnitudes thereof to be selected should be optimum forobtaining a film having a suitable thickness and a suitable constitutiondepending on the purpose or use thereof. Then, the minute metallicparticles were washed with the solvent used and methanol and the wetminute metallic particles were dried to complete the surface treatment.In a solution of 10 g of epoxy monomer (BPA) in 15 ml of ethyl acetate,10 g of the surface-treated minute metallic particles were stirred witha homogenizer at 150 rpm as illustrated in FIG. 11 to form a suspensionand induce a reaction to effect the coating of the surface of Ag/Cuparticles with an insulating resin layer.

Here, the principle of the production of the MC type conductive fillerwill be described below.

When a suspension is formed by dispersing minute metallic particles in asolution of triazine thiol in an organic solvent, this triazine thiolreacts with the OH⁻ group on the surface of the metallic particles toform a relevant salt. As a result, the surface of the minute metallicparticles is coated with a triazine thiol film. When a suspension isformed by dispersing the minute metallic particles treated will triazinethiol in a solution of the monomer, the surface of the minute metallicparticles undergoes a reaction. Consequently an MC type conductivefiller having the surface of minute metallic particles coated with thepolymer is obtained.

Now, the reaction mechanism involved herein will be described below.

The triazine thiol is a compound having a structural formula I shownbelow. ##STR1## (wherein R stands for a group represented by --SH,--N(CH₃)₂, --NHC₆ H₅, --N(C₄ H₉)₂, --N(C₈ H₁₇)₂, --N(C₁₂ H₂₅)₂, --N(CH₂CH═CH₂)₂, --NHC₈ H₁₆ CH═CHC₈ H₁₇, --NCH₂ C₆ H₄ CH═CH₂ (C₈ H₁₇), or--NHC₆ H₄).

When the minute metallic particles are subjected to a surface treatmentwith this triazine thiol, there ensues a reaction path in which amonomolecular film of triazine thiol is formed on the surface of theminute metallic particles in the first step and the monomolecular filmdevelops into a polymolecular film in the second step as illustrated inFIG. 12, with the result that the surface of the minute metallicparticles will be coated with the triazine thiol film. When the minutemetallic particles that have undergone the surface treatment are mixedwith an epoxy monomer, the triazine thiol acts as a cross-linking agentfor the epoxy monomer to undergo a reaction illustrated in FIG. 13 andgives rise to a cured product of epoxy. Consequently, an MC typeconductive filler having a surface of the minute metallic particlescoated with the epoxy resin is obtained.

Here, it is necessary to pay attention to the following points.

(1) The production of the triazine thiol film must be carried out in anatmosphere of nitrogen. (2) The triazine thiol concentration must be notmore than 10⁻³ mol/liter. (3) The reaction of the monomer must becarried out with the suspension stirred at a rate in the range between50 and 250 rpm. The reason for (1) is that the minute metallic particlesreadily undergo corrosion in the presence of air because they have alarge surface area. The reason for (2) is that the concentration of RTD(triazine thiol) must be kept below 10⁻³ mol/liter because the amount offilm is calculated from the amount of unreacted RTD. The reason for (3)is that the minute metallic particles settle and agglomerate during thereaction of the monomer when stirring is omitted.

(2) Observation of Cross Section of Capsule Type Minute MetallicParticles

The produced filler was embedded in the epoxy resin, allowed to cure,and cut with a microtome to expose a cross section of the capsule typeminute metallic particle to visual observation.

(3) Confirmation of Insulation with Capsule Type Minute MetallicParticles

The produced MC type conductive filler was agglomerated into a coheringmass and tested for insulation resistance with an insulation resistancemeter used at freely selected points of measurement.

(4) Production of Conductive Adhesive Agent

An MC type conductive adhesive agent was produced by mixing an MC typeconductive adhesive agent with 20% by volume of the MC type conductivefiller prepared in (1) above. The results of the test indicate theviscosity of the produced adhesive agent was so high as to jeopardizethe workability if the voluminal proportion exceeded 20%, the producedadhesive agent was barely usable if the voluminal proportion was up to60% of the MC type conductive filler, and the adhesive agent includedparts allowing no electric continuity if the voluminal proportion wasunduly small. Thus, the optimum content of the MC type filler is fixedat 20% by volume. Here, the adhesive agent used herein was aone-component type for facilitating the process of production.

(5) Union of Chip and Substrate

A substrate illustrated in FIG. 4 to which the conductive adhesive agentproduced in (4) above was applied and a glass chip (128 pins, 300 μmpitch, and electrode interval 100 μm) illustrated in FIG. 6 on whichstud bumps were formed were subjected to thermocompression bonding at175° C., 30 s, and 20 g/bump.

(6) Test for Electric Continuity and Test for Insulation

Samples of the product of union indicated in (5) above were tested forelectric continuity resistance by the four-terminal method using thepoints of measurement illustrated in FIG. 6 and FIG. 7 and tested forresistance with a resistance meter.

(Results)

(1) Observation of Cross Section of Microcapsule Type Conductive Filler

The condition of the surface of minute conductive particles coateduniformly with an insulating resin as illustrated by a type diagram ofFIG. 3 was confirmed.

(2) Insulation Resistance of Microcapsule Type Conductive Filler

The magnitudes of insulation measured at all the points invariablyexceeded a high level of 1×10¹¹ Ω.

(3) Measurement of Electric Continuity Resistance and InsulationResistance Between Bonded Chip and Substrate

The union between the chip and the substrate was obtained as illustratedby a type diagram in FIG. 10. The magnitudes of electric continuityresistance were satisfactory, invariably falling below 0.2 Ω per pointof contact. Though the filler was incorporated in such a largeproportion as 20% by volume, highly satisfactory insulation of 1×10¹¹ Ωwas found between the adjacent patterns.

This example represents one case of using tiazine thiol as an affinityagent. This invention is not limited to this particular affinity agent.Naturally, any compound possessing a reactive group that exhibitsaffinity for both the metal and the monomer intended to coat the metalcan be used as an affinity agent.

EXAMPLE 15

In the production of capsule type minute metallic particles by theprocedure of Example 14, the stirring of the suspension was carried outat varying rates of 30, 50, 250, and 300 rpm to determine the effect ofthe stirring speed on the stability of the suspension.

(Results)

Table 11 shows the effect of the stirring speed (30, 50, 250, and 300rpm) on the stability of the suspension. The results indicate that thestirring speed must be in the range between 50 and 250 rpm for the sakeof suspension stability.

                  TABLE 11                                                        ______________________________________                                        Relation between stirring speed                                               and suspension stability                                                      Speed of                                                                      stirring                                                                      (rpm)   30          50      250   300                                         ______________________________________                                        Suspension                                                                            Sedimentation of                                                                          Stable  Stable                                                                              Adhesion of minute                          stability                                                                             minute                    conductive particles                                conductive                to beaker wall                                      particles observed        observed                                    ______________________________________                                    

EXAMPLE 16

An MC type conductive filler and a capsule type conductive adhesiveagent were produced by following the procedure of Example 14, exceptthat alcohol was used in the place of acetone. They were evaluated inthe same manner as in Example 14.

(Results)

In all the items of evaluation, the results were nearly the same asthose obtained in Example 14.

This invention is constructed as described above, it enables an MC typeconductive filler coated with a thermosetting resin possessed of bettercharacteristic properties than a thermoplastic resin to be producedeasily at a low cost. Thus, this invention realizes a practical MC typeconductive adhesive agent excellent in reliability and performance.

What is claimed is:
 1. A process for producing a microcapsule-typeelectro-conductive filler, comprising the steps of:a first step oftreating electro-conductive metallic particles with a coupling agent,the amount of coupling agent being in the range of 0.1 and 10% byweight, based on the amount of metallic particles; a second step ofmixing the coupling agent treated metallic particles with a solvent inwhich bisphenol A epoxy resin is dissolved, to coat the bisphenol Aepoxy resin onto the surface of the electro-conductive metallicparticles; a third step of dispersing the mixture obtained from saidsecond step in an aqueous phase having a viscosity in the range ofbetween 20 and 10,000 cps and having tetraethylene pentamine dissolvedtherein, to form an aqueous suspension; and a fourth step of stirringsaid aqueous suspension at a rate in the range of 50 and 250 rpm topolymerize the bisphenol A epoxy resin and the tetraethylene pentanineto form an insulating resin on the surface of the metallic particles. 2.A process for producing a microcapsule-type electro-conductive filler,comprising the steps of:a first step of treating electro-conductivemetallic particles with a coupling agent, the amount of coupling agentbeing in the range of between 0.1 and 10% by weight, based on the amountof metallic particles; a second step of mixing the coupling agenttreated metallic particles with a solvent in which bismaleimide anddiazobicycloundecene are dissolved, to coat the bismaleimide onto thesurface of the metallic particles; a third step of dispersing themixture obtained from said second step in an aqueous phase having aviscosity in the range of between 20 and 10,000 cps and havingtetraethylene pentamine dissolved therein, to form an aqueoussuspension; and a fourth step of stirring the aqueous suspension at arate in the range of 20 and 10,000 rpm to polymerize the bismaleimideand tetraethylene pentamine to form an insulating resin on the surfaceof the metallic particles.
 3. The process according to claim 1, whereinin said fourth step, said bisphenol A epoxy resin and tetraethylenepentamine are polymerized by a catalyst or heating.
 4. The processaccording to claim 2, wherein in said fourth step, said bismaleimide andtetraethylene pentamine are polymerized by a catalyst or heating.